2014-03-06_REVISION - C1996083 (2)

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Susan Burgmaier C- 1996.083 TR -84 PAR 06 -Mar -2014 Page 2 of 5 Please address the requirements of 4.10.4(2) (minimum static FoS of 1.5) for this proposed reconfiguration of CMWDA #3. Based on previous stability analyses performed, this will include a consideration of the dissipation of pore pressures, if any, as the CMW is dewatered, over time. MILT 03/06: Buckhorn's response, while it does include a single block failure analysis, fails to make a compelling argument for excluding total strength (Undrained) conditions from consideration and does not discuss the dissipation (or lack thereof) of pore pressures. The Mar -2007 Buckhorn report is the stability analysis for CMWDA #3 currently approved in the permit, and any proposed changes to the models and variables evaluated in that report should be accompanied by a thorough rationale that references the original study and incorporates any new information. Please address the requirements of Rule 4.10.4(2) (minimum static factor of safety of 1.5) for the proposed reconfiguration of CMWDA #3, including a consideration of undrained conditions resulting from a lack of dissipation of pore pressures. Alternatively, a detailed rationale supporting elimination of Undrained analyses from consideration may be provided. 2 (33) MILT 01/07 (edited): Section 6.0 of the TR -45 (29- Mar -2007) Buckhorn report provides a list of seven recommendations "to fulfill assumptions made in our evaluation and to ensure an adequate safety margin for the gob pile ". Item 6 states, in part: "Gob must be placed at, or slightly below its optimum moisture content. Gob placed significantly above the optimum moisture content likely will not achieve adequate compaction or undrained shear strength." Item 7 follows with, "We also recommend implementation of a moisture content specification allowing moisture contents no greater than 4% above the optimum moisture content." There does not appear to be a commitment by BRL in the text portion of Volume XI to implement the moisture content recommendation. Please review the Recommendations made by Buckhorn in 2007, in light of the CMW compaction and moisture content results obtained, to date. Clarifying language in the "Placement and Compaction" portion of the permit would be beneficial. Also, Buckhorn may wish to provide an updated discussion of moisture content requirements / recommendations with any response generated for Item 1(32), above. MLT 03/06: Buckhorn's response focused exclusively on the compaction aspect of this item (the Division agrees that the required compaction is being achieved), but failed to address the issues of undrained shear strength and elevated pore pressures. These topics of concern are addressed in greater detail in my 25 -Feb -2014 Memo and Summary that were transmitted to Bowie under TR -85 and will also be included in our second adequacy review for TR -84.